The enzymatic mechanism(s) involved in the RNA-directed proviral DNA synthesis by the Rauscher leukemia virus (RLV) DNA polymerase will be investigated both in vitro and in vivo. Studies on the in vitro synthesis of DNA directed by RLV 70S RNA will be stressed, and will include an examination of the possible role(s) of viral and cellular proteins and RNase H activities as well as that of 70S RNA conformation. We will also determine the effect of changing cell growth status on the synthesis of proviral DNA by infecting RLV particles. The inhibition of RLV DNA polymerase activity by inorganic phosphate is a phenomenon we have found to be specific for mammalian type C viral DNA polymerases. We will further investigate this phenomenon, and also determine the mechanism by which the polymerase-associated RNase H is inhibited by phosphate. We have also recently found that the polymerase-associated RNase H activity is inhibited by RNA and will expand our inquiry to determine whether the observed inhibition might relate to a biological function. The high-molecular weight intracytoplasmic form of RLV DNA polymerase, which is present in tissue culture cells producing virus, will be fully characterized. Through such analyses, we will determine whether it represents a precursor polyprotein which is catalytically active, or a protein-polymerase complex of viral or cellular origin which might function in proviral DNA synthesis. The present or absence of a similar viral DNA polymerase form in vivo will be determined using the AKR mouse system.